Ferroelectricity in artificial bicolor oxide superlattices

The ferroelectric growth and properties of high-quality artificial bicolor oxide superlattices composed of two perovskites were analyzed. The bicolor superlattice were grown on a single-crystalline substrates by using pulsed laser deposition after growing conducting films as a bottom electrodes on a single-stepped TiO²-terminated SrTiO³(STO) substrates. The ferroelectric hysterisis loops are found to be affected by the leakage current or the trapped charges at interfaces while ionic displacements in the fully relaxed structure break the inversion symmetry and yield a new polarization in each unit cell. The superlattice shows a potential-energy surface with a single minimum at zero polarization while the ionic motions in ferroelectrics break the inversion symmetry and provide the net dipole moments for displacive ferroelectrics.